The present invention relates to an air spring for motor vehicles, and more particularly, to an air spring comprising a housing and a piston surrounded by the housing. The housing and the piston are configured to form guide surfaces for U-type bellows operatively arranged therebetween and acting in opposite directions. Each of the U-type bellows is arranged between a radially outer circumferential wall of the piston and a radially inner circumferential wall of the housing.
For the suspension of vehicle axles, two possible arrangements are generally known. Either the spring and the damper are arranged separately on a link, or the spring and the damper are arranged concentrically, i.e. as a spring/damper element, and are attached to a link.
In the first known arrangement when the spring and the damper are separate from each other, the spring element carries out every movement of the link on which it is arranged. Thus, the spring element is sometimes so greatly compressed that it bends out due to the compression forces acting at its ends. This bending-out, which also occurs in the bellows of an air suspension in the arrangement on the link, enforces the use of rigid bellows which dampen the extent of the bending-out.
In the concentric arrangement of the spring and the damper on a link, it is possible, with straight guiding of the air spring element, to use thinner bellows. As a result of this arrangement, however, disadvantages have to be tolerated with respect to the spatial arrangement of the vehicle which results, for example, in a loss of trunk space or higher production costs due to the relatively large space requirement of the spring/damper arrangement.
An air spring element described in U.S. Pat. No. 3,033,558 consists of a single piston and does not have the above-mentioned disadvantages of the two above-discussed known different arrangements. In this air spring element, however, a compensation chamber is also required, into which the volume of air enclosed in the spring element and squeezed during the deflection operation can escape. By the provision of an additional compensation chamber, both the production costs and the expenditure for assembly of the air spring element are increased considerably.
An air spring for motor vehicles is described in U.S. Pat. No. 4,493,481. This air spring has a closed spring volume and two active spring surfaces of different sizes which are pressurized in opposite directions, face away from each other, and are variable in their size depending on the spring path. The spring surfaces are supported coaxially against each other. The spring volume is formed by two U-type bellows which bound a common chamber and whose active surfaces facing away from each other are supported on rigidly interconnected spring pistons of different diameters. Thus, the deformations of the loops of the U-type bellows during spring movements result in changes in volume which approximately balance each other out. The spring force is transmitted, on one hand, by the spring piston and, on the other hand, by a casing assigned to the walls of the U-type bellows.
It is disadvantageous in the known air spring to have a tension rod which is passed through the closed spring volume. As a result, complex and expensive sealing devices are required between the tension rod and the closed spring volume in order in fact to keep the latter closed.
An object of the present invention is, therefore, to overcome the above-mentioned disadvantages of known arrangements and, in particular to provide in a cost-effective manner an air spring for motor vehicles which combines the advantages of the separate spring and damper arrangement.
This object has been achieved in accordance with the present invention by providing that the housing and the piston comprise a double ring body each having an inner ring and an outer ring connected by an annular collar. One ring body is located opposite the other in mirror image and engages axially over the other in a region of the U-type bellows such that the outer rings and the inner rings define an annular space to receive the U-type bellows.
By configuring the housing and the piston in each case as a double ring body with an inner ring and an outer ring connected by an annular collar in accordance with the present invention, the above-mentioned disadvantages of the separate spring/damper arrangement and of the concentric spring/damper arrangement can be avoided in a desirably simple manner because bending-out is prevented. The overall arrangement is constructed in a space-saving manner so that no disadvantages have to be tolerated in respect of the spatial criteria of the vehicle.
Additionally, the configuration of the air spring according to the present invention results in a compact construction which accommodates the air spring below the vehicle.
A further advantage of the present invention resulting from the arrangement of the U-type bellows to form a parallel guide of the piston inside the housing resides in the articulated link arrangement only having to be called upon in the case of relatively large deviations in the tilt angle.
By way of the connection of the air spring according to the present invention to the link by a piston rod which has a joint at each of its ends, a connection between the link and the air spring can be produced very rapidly and cost-effectively.